1. Field of the Invention
The present invention relates to the capture, storage, and retrieval of digital images. More particularly, the present invention relates to novel methods for storing and retrieving pixel data from a full-color RGB imaging array imbedded in a device such as a digital camera.
Furthermore, the present invention also relates to vertical-color-filter detector groups and arrays thereof. More particularly, the present invention relates to arrays of detector groups wherein each of the detector groups is a multi-layer junction structure to ensure that each pixel sensor in the array measures each of the three primary colors (R-G-B) in the same location.
Finally, the present invention relates to a device such as a digital camera that employs both an array of vertical-color-filter detector groups and a novel method of capturing, storing, and retrieving the data provided by the array.
2. The Prior Art
MOS active pixel sensors and multiple-wavelength sensors are known in the art. One type of multiple-wavelength sensor employs red, green, and blue sensors disposed horizontally in a pattern at or near the semiconductor surface. Color overlay filters are employed to produce the color selectivity between the red, green, and blue sensors. Such sensors have the disadvantage of occupying a relatively large area per pixel as these sensors are tiled together in a plane.
Another type of multiple-wavelength sensor employs more than one sensor in a vertically-oriented group. An example of an early multiple-wavelength vertical-color-filter sensor group for detecting visible and infrared radiation is disclosed in U.S. Pat. No. 4,238,760 issued to Carr, in which a first diode in a surface n-type epitaxial region is responsive to visible light and a second buried region in an underlying n-type substrate is responsive to infrared radiation. Contact to the buried photodiode is made using deep diffusion processes similar to diffusion-under-film collector contact common in bipolar IC processing and for RCS reduction. The disclosed device has a size of 4 mils square. An alternative embodiment employs V-groove MOS transistors to contact the buried p-type region of the infrared diode.
The device disclosed in the Carr patent has several shortcomings, the most notable being its large area, rendering it unsuitable for the image sensor density requirements of modern imaging systems. The technology employed for contact formation to the buried infrared sensing diode is also not suitable for modem imaging technology or extension to a three-color sensor.
A particular example of a three-color visible-light prior art vertical-pixel-sensor group is disclosed in U.S. Pat. No. 5,965,875 to Merrill. In Merrill, a structure is provided using a triple-well CMOS process wherein blue, green and red sensitive PN junctions are disposed at different depths beneath the surface of the semiconductor substrate upon which the imager is fabricated.
There is also the problem of processing, storing and retrieving digital data captured by a three-color vertical sensor group.
Generally, a digital image is provided from a source such as a camera. Many types of cameras are prevalent in the field of digital imaging, including digital photograph, video, and television cameras. Whatever type of camera is used, it is often desired that the image be captured and stored in a digital format, so that the image may later be edited or otherwise processed. In the prior art, it is common to interpolate and compress the digital image data prior to storage. Manipulating the data before storing it poses certain disadvantages that are inherent in the procedures utilized heretofore in the prior art.
First, the process of interpolation may introduce irreversible changes in the digital image data. Interpolation is the process of correcting the data for errors that occur by virtue of the type of camera or sensor utilized within the camera. Therefore, the type of interpolation that is used, or the need for interpolation at all, is determined by the nature of the imaging process being utilized. For example, some digital sensors contain Charge-Coupled Devices (CCD) or metal-oxide-semiconductor (MOS) transistors. The smallest resolvable full-color image component usually comprises for separate sensors: two green, one blue, and one red. These sensors are used to produce three-color digital output. However, interpolation is necessary to correct for distortions caused by small, though finite distances that separate the four individual sensors that make up each resolution element. The result of interpolation is often a substantial increase in the size of the original digital image. Most often the increase in size is three-fold. Along with an increase in size, interpolation can compromise the integrity of the original data if performed prior to storage.
Second, after the step of interpolation, the digital image data is often compressed prior to storage. Compression is necessary often because of the increase in size caused by interpolation. The compression must be performed to facilitate transmission through systems having limited bandwidth such as television systems. A problem with commonly used compression systems is that the original state of the image cannot be restored from the compressed data. This is a serious problem if use of the original image data is ever desired.
The problems with interpolation and compression prior to storage manifest as poor-quality output when the digital image is viewed on a screen or printed. In fact, interpolation and/or compression techniques often create moiré patterns on fine-pitched fabrics or result in loss of detail and/or distortions along the edges or between fine lines in the subject matter.
In the light of the above background, those skilled in the art desire an image storage and retrieval method that does not require interpolation and/or compression of a digital image data set.